The present invention relates to an apparatus for making underground passages.
It is well known to install underground pipelines to make tunnels, waste-disposal systems and the like, by digging ditches and installing cement or other pipes in these ditches whereupon the ditches are closed and the pipe is buried. However, there are applications where this approach cannot be used. For example, if such pipeline is to be installed in ground on which structures are already erected, such as if it is to traverse the ground beneath buildings or the like, it is evidently not possible to dig up the ground underneath the building. For such circumstances a different system has been developed according to which a pit is dug or otherwise provided at an appropriate location, and pipes are driven into a sidewall of the pit below ground level, being rammed forward by hydraulic presses or the like, so that they penetrate through the ground in the desired direction without any necessity for digging up the ground.
In this latter type of application it is important that the penetration of the pipes through the ground be facilitated as much as possible, and that the entry of soil into the pipes be prevented. For this purpose it is known to use an apparatus having a head which is secured to the leading end of the first pipe to be driven into the ground (which is followed by a string of successive pipes that are added to the trailing end of the first pipe) and which serves to displace the soil ahead of it as it penetrates the soil.
It stands to reason that these heads are subject to very high stresses as they are being driven into and through the soil, and that they must accordingly be of very strong construction. Heretofore, these heads have been made of heavy sheet steel parts which are welded to the desired configuration. This, however, involves considerable manufacturing expenses, since the steel must be of good quality ad is therefore expensive, and since the welding-together of the various sheet steel components to form a head of the desired shape is also expensive.